1. Field of the Invention
The present invention relates to a cooling apparatus for a heat exchanger provided for an automobile radiator and the like.
2. Description of the Prior Art
A shroud is provided for a cooling apparatus of an automobile radiator, and delivers an air flow resulting from a high speed rotation of a fan to the radiator efficiently. For instance, as illustrated in FIGS. 7, 8 and 9, this type of shroud comprises a box-shaped main body 101 covering one of the surfaces of a radiator 300 and a cylindrical portion 102 protruding from the main body 101. Further, a fan 200 is disposed in the cylindrical portion 102. When the fan 200 is driven rotationally, the air in the main body 101 is drawn in by suction, and a negative pressure is generated. The resulting negative pressure creates to an air flow which comes from the other surface of the radiator 300 and goes out through the cylindrical portion 102 by way of the one of the surfaces of the radiator 300.
Recently, noise reduction has been one of the major issues in the automobile industry as a part of a program for improving the habitability in an automobile passenger compartment. In a cooling apparatus for a heat exchanger, noise reduction during the rotation of the fan has been an important issue, and accordingly the configurations of the fan and the shroud have been investigated and researched extensively. Here, the following phenomenon is considered as one of the causes of the noise generation resulting from the shroud. Namely, shock noises are generated when part of the air flows, generated by the action of the fan and having directional vector components being not parallel to the axis of the cylindrical portion, collide with the inner surface of the cylindrical portion. In order to prevent the generation of the shock noises, a shroud having a noise absorbing chamber formed in the inner surface of the cylindrical portion is disclosed, for example, in Japanese Unexamined Utility Model Publication No. 153725/1982.
On the other hand, the following improvements have been carried out recently in order to improve the cooling performance, thereby keeping up with the increasing engine output. Namely, the radiator core has come to be made from a multi-layered structure, and the radiator fins have been provided with a high density and a short pitch, for instance. However, there arises a problem that these improvements have caused increased noise. In addition, the cylindrical portion 102 of the shroud should be disposed at a position deviating from the center of the radiator 300 as illustrated in FIGS. 7, 8 and 9, and part of the cylindrical portion 102 should be made in a configuration protruding with respect to the top of the radiator 300 because of the limitations in designing an automobile body. If such is the case, there also arises a problem of increased noise.